Current balancing transductors for parallel connected diodes



June 16, 1959 F. R. BINGHAM QURRENT BALANCING TRANsDucToRs FOR PARALLELCONNECTED DIoDEs Filed Dec 4 Sheets-Sheet 1 @zahl June 16, 1959 F. R.BINGHAM 2,891,212

CURRENT BLANCING TRANSDUCTGRS FOR PARALLEL CONNECTED DIODES Filed Dec.V14;, 1956 4 Sheets-Sheet 2 Y J2 34 *da f-a -40 Filed DeO. 14, 1956 June16, 1959 F R' B|NGHAM 2,891,212

`CURRENT BALANCING TRANSDUCTORS FOR PARALLEL CONNECTED DIODES 4Sheets-Sheet 5 June 16, 1959 ,Filed Dec. 14, 1956 F. R. BINGHAM2,891,212 CURRENT BALANCING TR-ANsDUcToRs FOR PARALLEL CONNECTED nIoDEs4 Sheets-Sheet 4 BY ma/fihi United States Patent O CURRENT BALANCINGTRANSDUCTORS FOR PARALLEL CONNECTED DIODES Francis R. Bingham,Norristown, Pa., assignor to I-T-E Circuit Breaker Company,Philadelphia, Pa., a corporation of Pennsylvania Application December14, 1956, Serial No. 628,325

9 Claims. (Cl. 321-27) My invention relates to a reactor means forforcing a predetermined current distribution between parallel connecteddiodes of the semi-conductor or metallic type as set forth in copendingapplication Serial No. 628,324 filed December 14, 1956 entitled CurrentBalancing Reactors for Rectifier Elements to Isadore K. Dortort andassigned to the assignee of the instant invention, wherein the reactorhas two cores of square loop hysteresis material which are biased inopposite directions.

Present advances in the construction of the various types of diodes suchas the metallic and semi-conductor type with the use of the germaniumand silicon elements has led to the increasing use of these members forhigh current capacity rectifying systems. Thus it is possible, in amultiphase rectil'ier system, to connect a number of diode elements inparallel for each phase, whereby D.C. current capacities of the order of5000 amperes may be obtained. Since, however, individual diodes vary intheir forward voltage charactceristics, the current distribution betweenparallel connected diodes will not be equal unless the diodes are veryclosely matched in these characteristics. Furthermore, diodecharacteristics are changeable with age, temperature conditions, andmany other uncontrollable parameters. Thus, even though the diodes mayoriginally have been closely matched to conduct substantially the sameforward current, this matching may be unbalanced after a relativelyshort period of operation.

The principal object of my invention is to provide a reactor means forforcing an equal or a substantially equal current distribution between aplurality of parallel connected diodes, even though their forwardconducting characteristics are not matched to one another.

Above noted copending application Serial No. 628,324, tiled December 14,1956 sets forth a reactor construction which is such that the forwardvoltage drop of any individual rectifier is automatically adjusted byinductive means depending upon the individual rectifier characteristicsso that the total current through each of the diodes is substantiallyconstant.

In one form of the above invention, a reactor system is providedcomprising a through-type balancing reactor in a so-called whiie treearrangement. Thus, a main current carrying bus is divided into twobranches. Each of these branches is then connected to form a first andsecond winding of a magnetic core, whereby the flux induced in themagnetic core due to the rst and second winding are in opposingdirection. Thus, if the current through the first branch exceeds thecurrent in the second branch by the magnetizing current of the reactor,the voltage of the first branch will be reduced, and the voltage in thesecond branch increased by an equal amount, and in just sutiicientamount to increase and decrease their currents respectively, so thatthey will diifer by no more than the required magnetizing current.

In a similar manner, if the current in the second branch exceeds thecurrent in the rst branch by the magnetizing 2,891,212 Patented June 16,1959 ICC current of the reactor, the voltage of the first branch will beincreased and the voltage of the second branch decreased.

It is to be noted that the iiux of the reactor during any conductivecycle is varied in only a single direction, this flux being decreased toits residual ux density during the blocking cycle of the respectiveseries connected diode. For this reason, the reactor cores should be ofthe type having a low residual magnetization wherein small air gapscould be utilized to achieve this end in the absence of special reactorcontrol systems as will be set forth hereinafter.

The first and second branch thus being balanced to carry a substantiallyequal current within the limits of the magnetizing current of thereactor may then each form a further first and second branch, each ofwhich is taken through a reactor in a manner similar to that describedabove. The outputs of these two reactors will then have four currentbranches wherein the current in each of the branches is substantiallyequal within the limits of the magnetizing current of their controllingreactors.

1f now a single diode is connected in each of the four output branches,then it is clear that they will each carry the same current magnitudediffering only by the magnetizing currents of their varying reactors,regardless of their individual forward voltage characteristics.

If it is now desired to further increase the current rating of thesystem, it is obvious that each of the four output branches could befurther subdivided with the use of further balancing reactors wherebyeight output branches would be provided at which points diodes would beconnected to carry an equally distributed load current.

A second embodiment of the above invention could comprise a simpleseries reactor connected in series with each of the individual diodeswherein each of the impedances are substantially equal and iixed and areof such a value that the reactor impedance drop is substantially largerthan the variations of forward resistance drop between diodes. Hence thevariation in forward resistance from diode to diode which results in thecurrent unbalance will be a smaller percentage of the total branchimpedance whereby the current unbalance from branch to branch will bereduced similarly and current balancing will result.

The construction of these series reactors is so simple as to possiblyoffset the disadvantage of decrease in power factor in the rectifiersystem due to their use. By Way of example, t'ne reactors could becomprised of a substantially U-shaped iron core which is simply slippedover a conductor in series with an associated diode, the air gap betweenthe adjacent ends of the reactor core providing a reactor which will notsaturate at peak forward current, and having the desired low residualmagnetiza tion to prevent the subsequent saturation of the reactor whichwould occur since this reactor is subject to repetitive uni-directionalpulses. If desired, this U-shaped lamination could be a substantiallycircular lamination having an air gap cut therein wherein laminationsare stacked around the conductor to be connected in series with thediode until the required reactor size is achieved.

In order to provide a more accurate balancing in the above describedsystem with less effect on power factor, using the inexpensive andcompact series reactor having only a single turn comprising the mainconductor for each diode, each reactor core may be provided with a smallsecondary winding wherein the secondary windings of each reactor areconnected in series to thereby reduce the effective impedance and stillforce proper current division within the limits of the magnetizingcurrents of the reactors in a manner similar to that described by thethroughstype reactor.

A still further embodiment of the above invention in application SerialNo. 628,324, filed December 14, 1956, would be in the utilization of thecouplet type reactor used in a chain or cascaded arrangement. Morespecifically, in the couplet type of system, the conductors of a" firstand second diode will be coupled by a magnetic core so that iluxes areinduced in the core in opposite directions. The conductor of a thirddiode is then coupled to the conductor of the second diode by a secondmagnetic core so that once again lluxes are induced in the secondmagnetic core in opposite directions by the currents in the second andthird diode conductors.

In the same manner, any desired number of conductors which includediodes which are to be connected in parallel may be added to the abovenoted chain by providing a magnetic core for coupling to adjacent diodeconductors so that the fluxes in the core will be induced in oppositedirections. So long as the chain arrangement is utilized and the iirstdiode conductor is not coupled to the last diode conductor added to thesystem, the maximum current imbalance between the individual diodescannot exceed the total magnetizing currents of all the core used minusone.

If, however, an even number of parallel connected diodes are used in theabove described chain, it is possible to close the chain by coupling thefirst and last diode conductor whereby the maximum current imbalancecannot exceed the magnetizing current of one-half the total num ber ofreactors. lf it is desired to reduce the current unbalance in thestraight chain relationship to the value of one-half the magnetizingcurrent given inherently in the closed chain arrangement, it is possibleto close the straight line arrangement even though an even number ofparallel elements are utilized by providing an extra core on each end ofthe straight line arrangement and to thereafter connect auxiliarywindings of each core to one another.

As has been pointed out above, it is necessary in each of the abovecases to utilize a reactor having a low residual magnetization since thetlux reversing operation on the reactor will be uni-directional and theoperation of the reactor will occur somewhere between its point ofresidual linx density and saturation tlux density. Thus, by providing alow residual magnetization for a low residual 'flux density, the corewill be able to achieve a relatively large flux change and may be maderelatively small as compared to cores having a relatively high residualmagnetization.

It would, however, be desirable to 'utilize a material of the grainoriented type, since magnetizing currents in these type cores isextremely low. il his would normally be prevented, however, since theresidual magnetization of these cores is extremely high as compared tothe heretofore described cores which could be constructed of normaltransformer steel and having air gaps therein.

I have found, however, that l can utilize cores of the highly grainoriented type by providing a first and second core for each reactorwherein the cores are biased to saturation by a D.C. bias in oppositedirections.

Thus, if the current ot one common conductor rises, one of the coreswill change in flux from a first saturation value to some value belowits saturation in the oppo* site direction, while the other core remainssaturated.

Conversely, it the current in the other conductor rises, the lastmentioned core will experience a iiux change and the first mentionedcore will be maintained saturated.

In each case, the cores will be returned to their initial oppositesaturations during the inverse voltage portion of the cycle so that theymay operate on the successive cycle.

Accordingly, the primary object of this invention is to provide improvedreactor means for forcing an equal. current distribution between aplurality of parallel connected 4 diodes wherein the reactor is of thetype having a relatively small magnetizing current.

A further object of this invention is to `utilize reactors having doublecores of square loop hysteresis material wherein each core is biased toan opposite saturation, the iirst core operating to decrease diodecurrent in a first of a pair of diode conductors, the second coreoperating to decrease diode current in a second of said pair of diodeconductors.

These and other objects of my invention will become apparent from thefollowing description when taken in conjunction with the drawings inwhich:

Figure 1 shows a single phase halfwave rectifier having a plurality ofdiodes connected in parallel.

Figure 2 shows the forward voltage characteristics of the diodes ofFigure 1.

Figure 3 shows the application of balancing reactors to the circuit ofFigure l for forcing a substantially equal current distribution betweenthe diodes.

Figure 4 shows the forward voltage drop on two of' the diodes of Figure1.

Figure 5 shows another embodiment of balancing type reactors.

Figure 6 shows a still further embodiment of balancing type reactors.

Figure 7 illustrates my novel invention wherein straight-throughreactors are applied to the circuit of Figure 1.

Figure 8 is an exploded perspective view showing the mechanicalconstruction of the through-type reactors of Figure 7.

Figure 9 shows the manner in which secondary windings may be applied tothe reactors of Figures 7 and 8 for forcing a more nearly equal currentbalance between their associated diodes while reducing the effect of thereactors on power factor.

Figure 10 shows an application of my novel invention wherein coupletreactors are applied in an open chain relationship.

Figure l1 shows a further application of the couplet type reactors to aclosed chain system.

Figure 12 shows how an open chain of couplet reactors for an odd numberof diodes may be connected in a closed chain relationship.

Figure 13 shows how an even number of diodes con nected in an open chainby couplet reactors may be connected in a closed chain relationship.

Figure 14 illustrates one possible physical arrangement of an open chaincouplet reactor system. Y

Figure l5 shows the bus and bus lianges of the de'- vice of Figure 14.

Figure 16 shows a view of Figure 15 when taken across lines 16-16.

Figure 17 shows a view of Figure 14 when taken across the lines 1717.

Figure 18 shows a View of Figure 14 when taken across the lines 18-18.

Figure 18A shows how the coupling reactors may be modified to allowconductor entrance to the bus of Figure 14 from the same side of the busrather than from alternate sides.

Figure 18B shows a side View of Figure 18A.

Figure 19 illustrates how the reactors of my novel. invention may beadapted to allow the use of high residual tlux density material havingrelatively low magnetizing current.

Figure 20 shows the magnetic characteristics of the ever, that the useof a single phase rectifying systemv isv to be taken for illustrativepurposes only, since my novel invention is clearly `applicable to anytype of rectifier` connection so long as diodes in any branch are to beconnected in parallel.

In a similar manner, while the'use of four parallel connected diodes hasbeen used for the most part in the following description, this numberhas been arbitrarily selected and my novel invention is equally adaptedin the paralleling of from two to any desired number of diode elementswhich are to have a substantially equal current flow therethrough.

Thus, Figure l shows a single phase A.C. voltage source 30 connected toenergize a D.C. load 32 through the parallel connected diodes 34, 36, 38and 40. The forward voltage characteristic of each of diodes 34 through40 is shown in Figure 2 where it is seen that since each of the diodesof Figure l has a forward voltage drop V1, the current through eachparallel branch is diierent. That is to say, diodes 34, 36, 38 and 40conduct currents having the magnitudes I1, I2, I3 and I4 respectively.

Clearly this unbalance in current distribution is due to the differencein the forward voltage characteristic of each of the diodes as isclearly seen in Figure 2.

The principle of my invention is to provide a reactor control meanswhich is so constructed that the currents in each of the parallelbranches will be forced to maintain a substantially equal distribution.Thus, reference to Figure 4 which, for illustrative purposes, shows thewave shapes of the forward voltage drops of the branches containingdiodes 34 and 36 of Figure 1 as voltage drops V1 and V2 respectively,these voltage drops are to be controlled by the reactor means of myinvention so that an equal current distribution will result. That is tosay, the reactor means operating on the current I2 will cause adifference in forward voltage drop for the two diode branches inaccordance with the voltage time area which is given by the shaded areaof Figure 4, this area being equal to the integral of V1 minus V2 whereV2 is the voltage drop on diode 36 times the differential in time. Thusthe diode currents may now be adjusted to the same value.

One type of reactor means which satisfies the above condition inaccordance with my novel invention is setv forth in Figure 3 wherein thecircuitry of Figure 1 has been modified to include the through-typereactors 42, 44 and 46 which are connected in a Whiffle tree typearrangement for forcing the desired current equalization. Morespecifically, the right hand end of source 30 is broken into a first andsecond branch which include Windings 48 and 50 respectively on the core42. These two windings are so connected that they will induce M.M.F.s inthe core 42 in opposing directions. Accordingly, as soon as themagnetizing current of core 42 is exceeded because of an unbalance inthe ampere turns of the ux due to a higher current in one winding, avoltage will be induced in winding 50 and the voltage in the branchwinding will assume a reactance and the current therethrough containingwinding 48 will be reduced until the currents in windings 48 and 50 areequal (within the magnetizing current of core 42).

Each of the two branches including windings 48 and 50 are then furtherbranched, the branch including winding 48 being subdivided into branchesincluding windings 52 and 54 while the branch including winding 50 issubdivided into the branches including windings 56 and 58.

Here again current equalization takes place in the branches includingwindings 52 and 54 and the windings 56 and 58 in the same manneras'previously described for windings 48 and 50. Thus, the current flowthrough diodes 34, 36, 38 and 40 will be substantially identical,differing only by the magnetization current of the cores acting thereonregardless of their forward voltage characteristics. Hence, if currentunbalance would normally exist between the diode branches includingdiodes 34 and 36, it is lseen that winding 54 will have induced in it avoltage of such a value to alter the 6 voltage drop across diode 36 to avalue V2, this voltage drop value being seen in Figure 2 to correspondto the current I1 which is the current flowing through the diode 34.Clearly diodes 38 and 40 will have their voltage drops similarlyadjusted to have their current magnitudes equalized to those diodes 34and 36 through the operation of windings 50 and 58.

Another type of balancing reactor system is set forth in Figure 5 whichshows a double Y secondary wherein the yneutral points of the Yconnected secondary windings 60 and 62 are connected through aninterphase transformer 64, the center of which is connected to one sideof 1a load 66. Each phase of secondary windings 60 and 62 is then takenout in the manner substantially identical to that shown in Figure 5 forthe case of phase A which is the only phase shown, in order to simplifythe diagram.

A multi-legged core (one leg for each rectifier element) is thenprovided for each of the phases wherein the D.C. component fluxes arecancelled out by having diametrically opposite ph-ases connected throughopposing windings. By way of example, phase A of winding 60 is connectedto the coils 68, 70 and 72 which are in turn connected in series withrectiers 74, 76 and 78 respectively which then connect to the oppositeside of load 66. In a similar manner, phase A is connected to windings80, 82 and 84 having their associated diodes 86, 88 and respectivelysimilarly connected to load 66.

In order to reduce the overall impedance and its effect on power factor7and improve voltage distribution, a polygon connected tertiary includingwindings 92, 94 and 96 is further provided. Clearly each of the threephases of the rectifying system of Figure 5 would be provided with asimilar three-legged core as that described in conjunction With phase A.

In operation, the interaction between windings 68, 70 and 72 of thebalancing reactor will maintain an equal current distribution betweendiodes 74, 76 and 78 in the same manner as has been set forth in thecase of Figure 3. Similarly, windings 80, 82 and 84 will maintain equalcurrent distribution between their associated diodes 86, 88 and 90respectively. Because of almost complete cancellation of D.C.ampere-turns, almost the com.- plete flux change can be utilized.

A similar arrangement may be provided for the three phase bridgeconnected rectifier system of Figure 6 where three parallel diodes areconnected in each leg of the bridge. If more than three rectifierelements are connected in parallel, the balancing reactor has more thanthree legs-one for each element. The tertiary winding is then connectedas a regular polygon. In Figure 6 a delta connected secondary winding 9Sfor energizing a D.C. load has a three-legged core which includeswindings 100, 102 and 104 for maintaining equal current distributionthrough diodes 106, 108 and 110 respectively. Similarly, windings 112,114 and 116 maintain equal current distribution between diodes 118, 'and122. Windings 112, 114 and 118 are moved in opposite polarity towindings 100, 102 and 104 to cancel the D.C. ampere turns. Once again,overall impedance is reduced, power factor improved, and voltagedistribution is improved by the delta connected tertiary which includeswindings 124, 126 and 128.

Clearly my novel invention has been shown in Figure 6 as applied to onlyone of the phases of secondary winding 98 and the other two phases willbe connected in a substantially identical manner.

Figure 7 shows how the circuit of Figure l could be adapted by reactancemeans of the series connected type. Thus in Figure 7, reactors 130, 132,134 and 136 are connected in series with diodes 34, 36, 38 and 40. Byconstructing reactances 130 through 136 so that they will have asubstantially higher impedance drop than the resistive drop of theircorresponding diodes 34 to 40 and further making the reactance ofreactors 130 through 136. a; substantially identical value, thenA thecurrent unbalancewhich isnow controlled by a much higher irripedancewill be substantially independent of the diode resistance inthe tforwarddirection thereby allowing a relatively. greatly. improved currentbalance between the diode, branches. This system is highly desirablesince it lends itself to extremely simple manufacturing techniques.

By way of example, Figure 8 shows that each of the reactors could becomprised of stacks of laminations 138, 140, 142 and 144 which haveopenings therein 'for allowing the passage of associated diodeconductors as well as air gaps such as air gaps 146, 148, 150 and 152respectively. More specilically, the device of Figure 8 shows the A.-C.source 30 as being connected in series with a. main bus 154 to whichconductors 156, 158, 160 and 162 are attached. Each of conductors 156through 162 is further provided with threaded ends which as will be seenhereinafter cooperate with fastening nuts 164 through 170 respectively.Each of conductors 156 through 162 therefore comprise a single turnwinding for the reactor' cores 138 through 144 respectively.

The individual diode assemblies 131i, 132, 134 and 136 are commonlyprovided with flexible conductors terminated by electrical connectingmeans 180, 182, 184 and 186 respectively, while their other ends areconnected to a second common bus 188 in any desired manner. Accordingly,by inserting conductors 156 through 162 through their respective`reactor cores and corresponding diode terminals 180 through 186respectively and thereafter tightening nuts 164 through 170 so as toachieve mechanical positioning of the reactors as well as electricalengagement of diode terminals 180 through 186 and conductors 156 through162, the A.C. source 30 may deliver rectified power to the llt-C. load32 as indicated in Figure 7. Clearly, the material utilized in coresl138 through 144 could be in laminated tform or solid form, dependingupon yallowable eddy current and hysteresis conditions.

Regardless of the type construction utilized in cores 138 through 144,however, it is necessary that air 146 through 152 respectively beprovided (in the absence of auxiliary means which are to be ascribedhereinafter) since it is necessary to avoid sat tion at peak forwardcurrents and to have a small i. .ual 'ilux density within the core `inview of the unidirectional cnergization thereof. That is to say, whilethe cere is operative, its fiux change occurs only from the point ofresidual magnetization to a point near saturation magnetization. Henceif as low as possible a residual magnetization is used, the core will becapable of a large flux excursion and would therefore be smaller thanone having a small ilux xcursion because of a high residualmagnetization.

As noted above, current balance between the various parallel branches inthe embodiment of Figure 7 is achieved by making the impedance ofreactors 130 through 136 high enough to malte the forward resistancedifferences of diodes 34- through d@ substantially negligible. It is,however, possible to modify the circuit of Figure 7 so as to force atrue current distribution between the parallel connected diodes which iswithin the limits of the magnetizing currents of the reactors.

This may be accomplished as set forth in Figure 9 wherein the reactorcores 138, 140, 142 and 144 which have air gaps 146, 148, 150 and 152respectively (see Figure 8) are provided with auxiliary secondarywindings 190, 192, 194 and 196 respectively, these secondary windingsbeing connected in series relationship. By this means all the reactorsare forced to participate in the correction of a deviation of current inany one rectier element, and there is a great reduction of the ellectiveimpedance of the reactors and their effect on power factor. In view ofthis connection, the current unbalancebetween any of diodes 34, 36, 38or 40 is held within the. limits of the magnetizing current of theassociated reactors, witlzxouttheundesirableeiectsV of straightreactors.

Figure 10 illustrates still another embodiment ofn'iy novell inventionwhereincouplet reactors are utilized, forcoupling the individual diodeconductorsA of parallel confnected branches. By way of example, Figure10` spel-ref.. matically illustratesa system of Vparallelconnecteddiodes,l wherein conductors 198,200, 202, 204, 2,06, 208,210`and 212 each have a single diode connected` in series, therewith, ThusVthe circuit corresponding to the` s chematic illustration of Figure10.would be similar'. tol'igure, 1 wherein eight rather than four diodesare connected in, parallel and areV to have equalcurrentdistributionim.- posed upon parallel connected diodes.

In Figure l0, however, coupled reactors 214, 2,16, 2,18, 220, 222, 224and 226 couple adjacent'branches oftheI parallel system in such a mannerthat the currenttlowin, adjacent branches is in opposite directions; asindicated by the dots and crosses ot conductors 198 througlr212y whichshow current ow into and out of; the drawing respectively.

Thus reactor 214 couples branches 198 and 200 in such, a manner that thefluxes induced in the core 214 due to conductors 198 and 200 are inopposing directions. In aV similar manner, reactor 216 couples branches;200. and?V 202, reactor 218 couples branches 202 and 204, and soon downthe line until the chain is completed by they cou. pling of conductors210 and 212 by the core- 226.

During operation of a circuit constructed in accord. ance with thecircuit of Figure` l0, the current unbalance will not exceed the totalmagnetizing current of all the cores. minus one, as is obvious inconsidering thearrange ment.

Here again, cores 214 through 226 should be of mate. rial having a lowresidual magnetism in order to` preventisaturation of the cores by anaccumulation of uni-direc,-v tional volt-seconds in successiveconducting periods.

If it is desired, a small air gap may be inserted in` each of the coresto lower its residual magnetism. How. ever, it is possible by auxiliarycircuitryto be described; hereinafter', to construct these cores of agrain Oriented material having an extremely low magnetizing cur-rent;yThis, of course, would be highly desirable since the maximum currentunbalance in the system of Figure 1-0 will be limited to the totalmagnetizing current of all the cores. minus one, as was set forth above.

In the event that there are an even number of parallel elements in thearrangement of Figure l0, it is. possible to close the loop as shown inFigure 11 by providing the additionalv core 228 which couples conductors212 and 198. In the closed loop, the maximum current uu. balance isdecreased from the case of the straight chain. to the magnetizingcurrent of one-half the total number of reactors. However, in theabsence of auxiliary equip.- ment, the loop can only be closed as seenin Figure 11 with an even number of conductors. For if an odd number ofconductors were used, the conductors at each end of the chain wouldconduct current in the same direc.- tion and `could not be directlycoupled to one another.

It is, however, possible to close a straight chain of either an odd oreven number of conductors by use of auxiliary reactors and auxiliarywindings therefor, as set forth in Figures l2 and 1'3. By` way ofexample, Figure l2 shows the manner in which a parallel group of. con.ductors corresponding to an odd number of diodes may be closed withouthaving to physically circle the configuration. It is to be noted thatthe configuration of` Figure l2 is substantially identical to that ofFigure 10 with the exception of the omission of core 226 and conductor212.

In order to allow closing of the chain or of the loop, the auxiliarycore 230 having an air gap 232 is coupledy to conductor `198 while core234 having an air gap- 2,36 is coupled to conductorv 210which is thelastgconductolj; oi the.v chain. Each of; cores-'2.30 and 2345 arefthgprovided with auxiliary windings 238 and 240 respectively which can beconnected to one another in any desired polarity so as to effect closingof the loop by a simple electrical connection which allows any desiredchoice of configuration of the chain, yet still providing the desiredcurrent balance which is limited to only one-half the magnetizingcurrent of all the cores.

. In a similar manner, the configuration of Figure 13 .which isidentical to that of Figure may close the loop by means of the same typeauxiliary reactors 230 and 234 having auxiliary windings 238 and 240which are connected as is required to achieve proper polarities of thefluxes in cores 230 and 234 with respect to the flux induced byconductors 198 and 212 respectively.

Here again, however, the coupling of the cores is achieved by purelyelectrical connecting means rather than by the physical configuration ofthe core, as was the case in Figure 11.

- Figures 14 through 18 show one method by which the open chainconstruction of Figure 10 could be accomplished in' a rectifier circuit.Figure 14 shows the A.C. voltage source 30, which is to deliver D.C.power to the load 32 as being connected to a bus bar 242 which, as isbest seen in Figures 15 and 16, has conducting flanges 244 and 246fastened thereto in any desired manner. If desired, the bus may behollow as shown in Figure 16 to allow passage of a cooling medium. Eachof flanges 244 and 246 is provided with alternate through holes andtapped openings so as to allow electrical connection by extensions ofconductors 196, 198, 200, 202 and 204 to pass through theircorresponding coupling reactors 214, 216, 218 and 220 (see Figure 10) inalternate directions.

Thus the flange plate 244, seen in Figure 15, has a through hole 248, atapped opening 250, a through hole 252, and then a further tappedopening 254 while ange plate 246 is provided with alternate tappedopenings which register with the through hole of flange plate 244 andthrough holes which register with the tapped openings 250 and 254 offlange plate 244.

Thus, as may be best seen in Figure 17, conductor 198 has a flexibleportion fastened to a conducting bolt member 256 which passes through athrough hole in flange plate 246 through the balance reactor cores 214and 216 and thereafter threadably engages flange plate 244 in a currentcarrying engagement. Conversely, the conductor 200 which was to initiatea flux in core 216 which is in a direction opposite to the fluxinitiated by conductor 198 passes through hole 248 of flange plate 244and then through the cores 216 and 218 and terminates in a threadedengagement with flange plate 246. Clearly, this alternate type ofconstruction is continued for each of the current conductors of theparticular rectitier phase in question.

Thus, although the rectiers associated with conductors 196, 198, 200 and202 and 204 which are each connected to the common bus 258 so as toproperly energize load 32, the current directions of the conductors of acommon coupling reactor are opposite to one another in order to allowthe desired current equalization or equal current distribution ofcurrent flowing through each of the parallel connected diodes.

If desired, the structure set forth in Figures 14 through 18 may beeasily modified so as to allow the conductor entrance through thereactor from the same direction or from the same side of the bus whileopposite fluxes may still be induced in the coupling reactors byconstructing these reactors to have the figure 8 shape set forth inFigures 18A and 18B. More specilically, Figure 18A shows a coupling core260 which could be used as any of the coupling cores 214 through 220 ofFigure 14 as being constructed of a roll of magnet Wire twisted in afigure 8 shaped and formed to nest in any desired manner as shown inFigure 18B. Clearly, by passing two conductors 262 and 264 through thetwo openings formed by the ligure 8 as seen in Figure 18A, each havingcurrent conduction in Vthe same direction will give rise to opposingfluxes within the core 260. While Figures 18A and 18B show thisconfiguration as being formed by a roll of magnet wire, it could clearlybe constructed of punched and formed laminations and could, in fact, beconstlucted in any desired manner so long as the residual magnetizationis relatively small.

As has been heretofore mentioned, it would be desirable to use a reactorcore in any of the above applications of material having as low aspossible a magnetizing current since the current unbalance from diode todiode is usually dependent upon this magnitude of magnetizing current.However, it is well known that cores exhibiting very low magnetizingcurrents such as the square hysteresis loop type of core also exhibit:an extremely high residual flux density. This high residual ux densityis extremely undesirable for applications of my novel invention since itwould require an extremely large core if the core is to be kept fromsaturating due to the accumulation of unidirectional energization.

I have found, however, that by forming each reactor of a first andsecond core of square hysteresis loop material and thereafter biasingeach core in an opposite direction, then one core will operate With verylow magnetizing current on an ampere turn unbalance in la rst directionwhile the other core will operate on an ampere turn unbalance in theother direction.

A preferred embodiment of my novel invention using a double core is setforth in Figure 19 wherein a threephase Wye connected transformerwinding 270 is to energize a D.C. load 271.

For purposes of clarity, only phase A of the rectier system is shown inFigure 19 and comprises the diodes 272, 274, 276 and 278 and the coupletreactors shown generally by numerals 280, 282 and 284. It is to be notedthat reactor 280 couples diodes 272 and 274, reactor 282 couples diodes274 and 276, `and reactor 284 couples diodes 276 and 278 in a mannersimilar to that described for the open chain couplet system describedhereinabove, this system being chosen for illustrative purposes only.

Each of reactors 280, 282 and 284 are further seen to be comprised oftwo magnetic cores (which are of square hysteresis loop type material)through Which extends the diode conductors and each having an auxiliarybiasing winding. Thus, reactor 280 has a first and second core 286 and288 which have biasing windings 292 and 290 respectively.

Similarly, reactor 282 is comprised of cores 294 and 296 having biasingwindings 300 and 298 respectively while reactor 284 has cores 302 and304 which have biasing windings 386 and 308 respectively.

Each of the biasing windings 290, 292, 298, 300, 306 and 308 are thenconnected to a source of biasing potential 310 which caused the twocores of each reactor 280, 282 and 284 to be biased in oppositedirections of saturation.

The operation of this novel system may -now be considered for reactor280 in view of Figure 20 which shows the characteristics of any of thereactors 288, 282 or 284. Assume first that reactor core 286 is biasedto the right of the point of Zero current difference between currentsthrough diodes 272 and 274 by D.C. bias energization Nlm of Winding 292due to bias means 310.

In a like manner, core 288 is oppositely biased by N131() to the left ofzero current difference by means of energization of winding 290.

In operation, if the current through diode 272 exceeds that throughdiode 274, by the amount of Nlm plus the magnetizing current of core 286then as seen in Figure 20, there will be a positive net difference inampere turns that will cause reactor core 286 to begin to execute a fluxchange and therefore decrease the forward voltage on diode 272 anddecrease the net current through that parallel branch.

1'1 In asimilar manner, too high a current through diode 274 will causeunsaturation of core 288 which thereby decreases the current in thebranch including diode 27 4.

Clearly, reactor 282 operates in the same manner to equalize currentsthrough diodes 274 and 276 while reactor 284 operates on diodes 276 and278.

Thus it is seen that current equalization proceeds within limits givenby the very small magnetizing current of reactors cores 286, 288, 294,296, 302 and 304.

Although I have here described preferred embodiments of my novelinvention, many modifications and variations will now be obvious tothose skilled in the art and I prefer therefore to be limited, not bythe specilic disclosure herein, but only by the appended claims.

I claim:

1. A current balancing system for a plurality of parallel connecteddiodes, said current balancing system comprising a reactor meansconnected in series with each of said parallel connected diodes; saidreactor means being constructed to adjust the forward voltage drop onits corresponding diode until the forward currents of each of saiddiodes are substantially similar regardless of their forward voltagecharacteristics; each of said reactor means comprising a first andsecond core of high permeability material, each of said first and secondcores being biased in opposite directions.

2. A current balancing system for a first and second parallel connecteddiode, said current balancing system comprising a first and secondreactor winding connected in series with said first and second parallelconnected diodes; said reactor windings being constructed to adjust theforward voltage drop on their said corresponding diodes until theforward current through each of said diodes is substantially similarregardless of their forward voltage characteristics; said first andsecond windings being wound on a first and second common core of squarehysteresis loop material in directions to induce opposing fluxes in saidcores, `and biasing means for said first and second core, said biasingmeans being constructed to produce biasing flux in said first core in afirst direction and to produce biasing flux in said second core in asecond direction.

3. The current balancing system of claim l wherein either said first orsecond core is capable of iiux change throughout the forward voltagecycle of said diodes.

4. The current balancing system of claim 2 wherein either said first orsecond core is capable of flux change throughout the forward voltagecycle of said diodes.

5. In a rectifier system for energizing a D.-C. load from an A.C.source, said rectifying system including a plurality of parallelconnected diodes for achieving a predetermined current rating, a currentbalancing system for forcing a substantially equal current distributionbetween each of said plurality of diodes; said current balancing systemcomprising inductive means connected in series with each diode of saidplurality of diodes; said inductive means being constructed to adjustthe forward voltage across each of said diodes to force equal currentthrough each of said diodes regardless of the forward voltagecharacteristics of said diodes, said induci tive means being operativethroughout the forward voltage conduction cycle of said plurality ofdiodes; said inductive means including a rst and second core and biasingmeans therefor, for biasing said first core in a first direction and forbiasing said second core in a second direction.

6. In a multiphase rectifier system for energizing a D.C. load from amultiphase A.C. source, each phase of said rectifying system including aplurality of parallel connected diodes for achieving a predeterminedcurrent rating, a current balancing system for forcing a substantiallyequal current distribution between each of said plurality of diodes;said current balancing system comprising inductive means connected inseries with each diode of said plurality of diodes; said inductive meansbeing constructed to adjust the forward voltage across each of saiddiodes to force equal current through each of said diodes regardless ofthe forward voltage characteristics of said diodes, said inductive meansbeing operative throughout the forward voltage conduction cycle of saidplurality of diodes; said inductive meansincluding a first and secondcore and biasing means therefor for biasing said first core in a firstdirection and for biasing said second core in a second direction.

7. A current balancing system for a plurality of parallel connecteddiodes, said current balancing system comprising a reactor meansconnected in series with each of said parallel connected diodes; saidreactor means being constructed to adjust the forward voltage drop onits corresponding diode until the forward currents of each of saiddiodes are substantially similar regardless of their forward voltagecharacteristics; said reactor means comprising a couplet reactor formagnetically coupling conductors connected to each of said plurality ofdiodes into pairs; the conductors of each of said pairs being directedto induce opposing fluxes in their respective couplet reactors, each ofsaid couplet reactors having a first and second core biased in a firstand second direction.

8. The current balancing system of claim 7 wherein said couplet reactorsform a closed chain.

9. The current balancing system of claim 7 wherein said couplet reactorsform an open chain having a first and second auxiliary couplet reactorconnected to the hrst and last diode conductor respectively of saidchain; each of said auxiliary reactors having auxiliary windings thereonconnected in series to close the chain.

No references cited.

